1.Field of the Invention
The invention relates to an exhaust gas turbocharger for an internal combustion engine, consisting essentially of a turbine and a centrifugal compressor, which are both arranged on a common shaft, whereby a vaned diffuser adjoins the compressor impeller driven by the turbine and whereby an auxiliary air drive, which is fed from an external compressed air source, is provided in the compressor part.
2.Discussion of Background
The acceleration behavior of the turbocharger when the internal combustion engine, for example a diesel engine, comes on load has to be improved by means of the auxiliary air drive in such exhaust gas turbochargers. The auxiliary air is then, as a rule, introduced into the compressor impeller. For this purpose, driving jets emerging from a plurality of nozzles are directed onto the impeller vanes. This can excite the vanes to vibrate. The danger of surging in the compressor impeller, latently existing due to the auxiliary air introduced, limits the air quantity delivered to the internal combustion engine and this acts against the desired acceleration effect. Flat inlet angles are therefore provided, particularly for reasons of vibration. Flat inlet angles, however, generate little drive. With increasing rotational speed, the inlet angle, and therefore the driving force, becomes smaller and smaller. In addition, the auxiliary air quantity must be limited for excitation reasons.
An exhaust gas turbocharger of the type mentioned at the beginning is, for example, known from DE-C1-35 04 465. A plurality of nozzle passages branch off from a compressed air collecting space arranged in the compressor casing. Compressed air is specifically directed onto the compressor impeller via these nozzle passages when required. Blading additional to the normal blading is provided, for this purpose, on the compressor impeller. This blading consists of auxiliary drive vanes evenly distributed around the periphery. The axes of the nozzle passages are directed onto the auxiliary driving vanes at an angle optimizing the ejector effect.